Question

In an NPN power transistor, the emitter current is $20mA$. If $98\%$ of the electrons injected in to the base region reach the collector, the base current is nearly

• A. $2mA$
• B. $1mA$
• C. $0.6mA$
• D. $0.4mA$

Answer 1

The correct option is D

$0.4mA$

Step 1: Given data

It is given that emitter current,

$I_E=20mA$

$98\%$ of the electrons injected in to the base region reach the collector,

Step 2: To find

The base current,$I_B$

Step 3: Calculation

Since $98\%$ of the electrons reach the collector, the collector current is $98\%$ of the emitter current and the base current is $2\%$ of the emitter current

As the collector current is nearly equal to the emitter current, the base current is $2\%$ of the collector current.

Base current,

$$\begin{gathered} I_B=2\%of{I}_E \\ \Rightarrow I_B=\frac{2}{100}\times 20 \\ \Rightarrow I_B=0.4mA \end{gathered}$$

The base current is $0.4mA$.

Option D is correct.